None is Python's value for "nothing here". A function that ends without return gives back None, and so does print.

def find_user(name):
    if name == "ada":
        return "Ada Lovelace"

user = find_user("bob")
if user is None:
    print("not found")
result = print("hi")
print(result)  # None

There is only one None object, so test for it with x is None and x is not None, not with ==.

x or default gives default whenever x is false. That covers None, but also 0, "" and [], which are often real answers:

count = 0
print(count or 10)  # 10, wrong
if count is None:
    count = 10
print(count)        # 0, right

Use None to mean "not given" or "not found", and check it with is None. Then a zero, an empty string or an empty list stays what it is.

Write describe_score(score) returning "no score" when score is None and f"score: {score}" otherwise, where 0 is a real score. Write pick(value, default) returning default only when value is None, and value otherwise.

The explanation opens here once every check passes.